The purpose of this investigation will be to study the effects of physical training as a protective agent against the degenerative changes that occur in the myocardium during chronic exposure of animals to a pressure overload and in a strain of hamsters (BIO 14.6) that develop a spontaneous myopathy. Both conditions lead to hypertrophy and subsequent heart failure. A major effort will be directed towards elucidating changes that occur in the contractile protein myosin, the excitation-contraction coupling system, energy production by the major energy producing pathways, and in the contractility of the heart. Myosin will be studied from the standpoint of its ATPase activity and molecular changes that occur. Calcium uptake and binding will be examined in the sarcoplasmic reticulum. Experiments will also be conducted with hormone deficient animals to ascertain whether the changes that occur in response to the exercise training are influenced by the major hormones.